The invention relates to reducing noise in an imaging system.
Referring to FIG. 1, a typical digital camera 12 uses a rectangular array of pixel sensors 13 to electrically capture an optical image 11. To accomplish this, a shutter (not shown) of the camera 12 momentarily exposes the image 11 to the sensors 13 for a predetermined exposure time. After the exposure, each sensor 13 indicates an intensity of light from a portion of the image 11.
The camera 12 typically processes the indications (provided by the sensors 13) to form a frame of data (which digitally represents the captured image) and transfers the frame (via a serial bus, for example) to a computer 14 for processing. For video, the camera 12 may capture several optical images and furnish several frames of data, each of which indicates one of the captured images. The computer 14 may then use the frames to recreate the captured video on a display (not shown).
Typically, the frame of data does not indicate an exact duplicate of the captured optical image due to imperfections introduced by the camera 12. As examples, the camera 12 may introduce optical distortion and noise. One type of noise may be dark current noise which may be defined as a random noise present in a captured dark image. The noise may be introduced by, for example, the sensors 13.
Circuitry of the camera 12 might be used to compensate for the dark current noise. However, compensation by the camera 12 may present difficulties. For example, circuitry to perform the noise compensation typically increases the complexity and cost of the camera 12. As another example, quite often, in an attempt to cancel out the noise from a particular pixel sensor, the camera 12 may subtract a predetermined noise level from the intensity that is indicated by the sensor. The predetermined noise level might be determined from, for example, an extra pixel sensor that is never exposed to light and might be used to set a predetermined noise level for a group (a row, for example) of the pixel sensors. However, the actual noise present at each pixel sensor might be substantially different from the predetermined noise level and thus, this type of compensation may be inaccurate.
Thus, there is a continuing need for a digital imaging system that reduces the cost and complexity of a digital camera and more accurately compensates for noise.
In one embodiment, a method includes generating a noise frame of data that indicates a dark current image. Video frames of data are also generated that indicate video images, and the video frames include noise. Information from the noise frame is used to compensate for the noise of the video frames.
In another embodiment, a method includes generating noise frames of data that indicate dark current images. Video frames of data are also generated that indicate video images, and the video frames include noise. The noise frames are time-multiplexed with the video frames to form a video data stream. The stream includes intervals in which at least one of the noise frames is followed in time by one or more of the video frames. The video data stream is received, and for each interval, information from the noise frame is used to compensate for the noise in one or more of the video frames.